1. Field of the Invention
The present invention is directed to the field of air conditioning systems, particularly vehicle air conditioning systems.
2. Description of Related Art
Vehicles are commonly equipped with air conditioning systems so as to provide comfort to the vehicle's driver and passengers on hot summer days. An air conditioning system includes an air compressor which is powered by the vehicle's motor, for driving a highly-volatile refrigerant through a system that includes a condenser, an expansion valve and an evaporator, as is well known. In a typical vehicle air conditioning system, fresh outside air is brought into the system and cooled down, after which it is blown into the vehicle cabin.
Several conditions influence the performance and efficiency of an air conditioning system, such as ambient temperature and humidity. Under hot, humid ambient conditions, the air conditioning system performs work to cool down and remove moisture from the fresh air to obtain a desired temperature and humidity within the vehicle. This fresh air is continually being added to the already-cooled air in the vehicle cabin. Since air is continually flowing in, the air conditioning system creates a positive pressure within the vehicle cabin, and so the already-cooled and dried air is continually seeping out of the vehicle cabin, resulting in air cooling losses. Thus, the air conditioning must perform constant work just to maintain a desired level of temperature and humidity within the vehicle cabin.
However, a vehicle air conditioning system is powered by the vehicle engine, and so the increased operation of the air conditioning system contributes to the engine load, which results in the consumption of additional fuel, thereby reducing fuel efficiency. It has therefore been previously contemplated to recirculate the already-cooled air in the vehicle cabin into the air conditioning system. This approach maintains the temperature and humidity level of already-cooled air, and reduces the cabin air cooling losses, and thereby reduces the load of fresh air coming into the system. As shown in FIG. 1A, a typical air conditioner blower case 10 of this type operates in a “fresh air” mode where a first damper 12 and a second damper 14 are both opened to a first position to allow fresh air from outside the vehicle cabin to enter the blower case 10. Incoming fresh air flows past the dampers 12, 14, through a subjacent filter 17, and the blower fan 16, and into the passenger compartment. In a “recirculation” mode, as shown in FIG. 1B, the first damper 12 and second damper 14 are both opened to a second position to allow air from inside the vehicle cabin to be drawn into the blower case 10 and through the filter 17 by the blower fan 16, and then returned to the passenger compartment. When the dampers 12, 14 are in this second position, they make contact with a rail 18, formed in the top of the blower case 10. The rail 18 insures an air-tight seal against the fresh air coming in from the outside the vehicle, and only allows vehicle cabin air to recirculate into the blower case 10. However, the rail 18 is spaced vertically from the filter 17, and does not serve to effectively separate the two incoming air streams. While this is not a problem when the both dampers are in the fresh or recirculation positions, this lack of separation of the two incoming air streams makes it practically impossible to have a partial recirculation of cabin air.
With standards and regulations governing clean air and fuel conservation, it is highly desirable to reduce fuel consumption wherever possible, particularly if this goal can be attained without a reduction in performance or end-user expectations. It would be highly desirable to control the amount of recirculated air, and/or provide a mixture of recirculated and fresh air, for the purpose of reducing air cooling losses under a variety of ambient environmental conditions. However, it has heretofore not been possible to selectively control quantities of recirculated and fresh air. For example, in the known system shown in FIGS. 1A and 1B, if vehicle cabin air is recirculated into the blower case 10 by opening one damper to the second position (recirculation) while the other damper is in the first position (fresh) when the vehicle is moving quickly, the fresh air flow produced by the vehicle's motion is much more powerful than the blower fan 16, thereby swamping out the recirculation air flow. More specifically, due to the lack of a sealing connection between the blower box and the filter 17, the incoming fresh air stream is not isolated or contained to the subjacent portion of ht filter, but rather flows under the rail 18 and flows through the entire filter surface. Therefore, in the prior art it is very difficult to control the flow of fresh air and the benefit of the recirculated air is not obtained.
Moreover, partial recirculation (i.e., returning air to the cabin consisting of a portion of fresh air and a portion of recirculated air) is not possible in the prior art construction.